Apparatus for replenishing developer in an electrophotographic system



March 11, 1969 R. R. ULARY APPARATUS FOR REPLENISHING DEVELOPER IN ANELEGTROPHOTOGRAPHIC SYSTEM Filed Sept. 28, 1967 R mY Hum A v Arm n!United States Patent US. Cl. 118-637 15 Claims Int. Cl. G03g 15/10; Bb5/02; 1305c 11/10 ABSTRACT OF THE DISCLOSURE Apparatus for replenishingprincipal developer, originally present in an electrophotographic systemin the form of a solid meltable body, comprises a container for holdingsolid melta-ble replenisher developer. Heating means within thecontainer are energized periodically to melt small portions of thereplenisher developer as the principal developer is consumed. Thecontainer is formed with a lower opening and disposed so that the smallportions of molten replenisher developer can fall through the loweropening onto the principal developer to replenish the latterperiodically.

Background of invention This invention relates generally to apparatusfor replenishing developer material in an electrophotographic system.More particularly the invention relates to improved apparatus forperiodically replenishing principal developer, originally present as asolid meltable body, in an electrophotographic system. The improvedapparatus is particularly applicable to electrophotographic systemsemploying solid (hot-melt) developers of the electroscopic typedescribed in US. Patent No. 3,079,272, issued to H. G. Greig, on Feb.26, 1963, for Method of Developing an Electrostatic Image.

By the term hot-melt developer, as use-d herein, is meant a developerthat is solid at normal room temperature and that comprisesfinely-divided electroscopic toner particles dispersed in anelectrically-insulating thermoplastic carrier material having a meltingpoint substantially Within a range of, e.g., from 50 C. to 200 C.

In electrophotographic systems wherein hot-melt developer is used in amolten state to develop a charge pattern on an insulating surface, ithas been found desirable to replenish the developer periodically as itis consumed in the developing process. For the optimum and reproducibledevelopment of charge patterns, it has been found desirable to maintainthe hot-melt developer at a substantially constant quantity or level.Unless the quantity of hot-melt developer, however, is continuouslymonitored and corrected in such electrophotographic systems, thequantity of developer material can vary from excessive to exhausted,thereby affecting the quality of development and the optimum operationof the apparatus involved.

Summary of the invention Briefly stated, the improved replenishingapparatus comprises means for adding replenisher hot-melt developer toprincipal hot-melt developer originally provided as a solid body inapparatus for developing an electrostatic image on an insulatingsurface. The improved replenishing apparatus comprises a container forsolid replenisher hot-melt developer. Heating means Within the containerare energized periodically to melt portions of the replenisher hot-meltdeveloper as the principal hotmelt developer is consumed during thedeveloping process.

3,431,890 Patented Mar. 11, 1969 The container is disposed so that anopening therein permits quantities. of molten replenisher hot-meltdeveloper to be added automatically and periodically to the principalhot-melt developer.

In a preferred embodiment of the improved replenishing apparatus, theheating means are energized at least once during the formation of eachimage on the insulating surface so that a small quantity of replenisherhotmelt developer can be added to the principal hot-melt developer tocompensate the latter for the quantity of hotmelt developer consumed inthe development of the image.

Brief description of the drawing FIG. 1 is a schematic drawing ofautomatic apparatus for developing an electrostatic image on aninsulating surface, utilizing the improve-d replenishing apparatus foradding replenisher hot-melt developer periodically to principal hot-meltdeveloper;

FIG. 2 is an enlarged, fragmentary, perspective view of a portion of theapparatus shown in FIG. 1, illustrating details of the replenisherhot-melt developer means and the principal hot-melt developer means;

FIG. 3 is a cross-section of the container of FIG. 2 for replenisherhot-melt developer, taken along a vertical plane parallel to, andadjacent, a side of the container, and viewed in the direction indicatedby the arrows 3 in FIG. 2, the hot-melt developer being shown inphantom, and

FIG. 4 is a cross-sectional view of the container for the replenisherhot-melt developer, taken along the line 44 in FIG. 3, the replenisherhot-melt developer being shown in phantom.

Description of a preferred embodiment Referring, now, particularly toFIG. 1 of the drawing, there is shown apparatus 10 for developingelectrostatic latent images (or charge patterns) on a photoconductiveinsulating surface 11 of an electrophotographic recording medium 12 by(principal) hot-melt developer 14. The recording medium .12 comprises aweb of relatively electrically conductive backing paper 13, 'havingthereon the insulating surface 11 of a photoconductive material, such aszinc oxide.

The recording medium 12 is pulled from a supply roll 16 by an idlerroller 17 and a driven roller 18, driven by a motor 19 coupled to theroller 18 by any suitable means. The recording medium 12 is thus pulledpast a charging station 22, an exposure station 24, and a developingstation 26 of the apparatus 10, in the direction of the arrow 28. Withthe exception of the use of the hotmelt developer 14, the method ofdeveloping electrostatic images by the apparatus 10 is described in anarticle, Electrofax, Direct Electrophotographic Printing on Paper, by C.J. Young and H. G. Greig, RCA Review, De-, cember 1954, vol. XV, No. 4.

The recording medium 12 is charge-d at the charging station 22 with asuitable electrostatic charge from a suitable unidirectional powersupply 30 The power supply 30 is capable of providing about :6000 voltswith respect to a reference potential, such as ground. Thephotoconductive insulating surface 11, if zinc oxide, is usually chargeduniformly negatively, as from a corona discharge device 32, and thepaper backing is charged uniformly positively, as from a coronadischarge device 34. The electrostatic charging operation is performedin the absence of light.

The uniformly-charged photoconductive insulating surface 11 of therecording medium 12 is exposed with a light image, as from a projectionof light through a photographic slide in a photographic enlarger 36, todischarge the uniform negative electrostatic charge selectively, inaccordance with the amplitude of light from the projected image. Thus,there is formed a latent electrostatic image on the photoconductiveinsulating surface 11.

At the developing station 26, the latent electrostatic image isdeveloped by the principal hot-melt developer 14, in a manner to bedescribed hereinafter in detail. The electrostatic image developed bythe hot-melt developer 14 is substantially self-fixing so that noadditional fixing or glossing operations are necessary. The developedimage on the recording medium 12 now moves in the direction of the arrow38 and may be cut from the web by any suitable means, as desired.

The projector 36 is energized from a source of suitable electricalenergy connected to a pair of terminals 42 and 40. The terminal 40 isconnected to the projector 36 through a normally open switch 46. Theswitch 46 is actuated at an appropriate time, and for a suitableduration, by a control circuit 48, in a manner well known in the art ofautomatic electrophotographic systems of which the apparatus is one. Apair of terminals YY is connected to the terminals 42 and 44,respectively, through the switch 46 for the purpose hereinafterappearing.

The motor 19 is energized, through a switch 50, from a source ofsuitable electrical energy applied to a pair of terminals 52 and 54. Theswitch 50 is also actuated by the control circuit 48 to control themovement of the recording medium 12 as desired in the apparatus 10. Awinding 56 around a field pole piece 58 of the motor 19 has a pair ofterminals XX for the purpose hereinafter appearing.

The hot-melt developer 14 is a solid at room temperature. When heated tomelting and applied in the molten form to a (latent) electrostatic imageon the recording medium 12, the developer 14 functions substantially asa liquid developer and the electrostatic image is developed to a visibleimage and substantially fixed. The hot-melt developer 14 comprises amixture of (1) a low melting carrier material which upon heating becomesquite fluid and which is electrically-insulating in character, and (2) adispersed phase in the carrier material of finely-divided tonerparticles. The hot-melt developer 14 has a melting point preferablybetween 50 C. and 200 C. and a viscosity not in excess of about 500centipoises at a temperature within that range. The toner particles maycomprise liquid droplets or solids, but they should be substantiallyinsoluble in the carrier material, and, when dispersed therein, shouldhave an electrical characteristic such that it takes on an electricalcharge. A number of examples of suitable hot-melt developers aredescribed in detail in the aforementioned US. Patent 3,079,272.

A typical hot-melt developer, for example comprises paraffin wax(melting point 55 C. to 79 C.) and carbon black. Finely-divided carbonblack is dispersed in the melt of the wax in proportions of up to 5parts by Weight of carbon black and 95 parts by weight of wax. Themixture is continuously stirred until a uniform dispersion is obtained.The mixture is then allowed to cool to form a solid block or cakedeveloper. Such a developer, when remelted and applied to a surfacebearing an electrostatic image, will develop that image as a result ofthe electrophoretic deposition of carbon black particles in the chargedareas of the image. This hot-melt developer will, during development,provide a smooth glossy finish on the photoconductive insulating surface11.

Referring, now, paticularly to FIG. 2, the principal hot-melt developer14 is shown in a container or trough 60. A hollow idler roller 62 isdisposed to rotate about its axis so that its peripheral surface 63extends into the trough 60. A stationary electrical heating element 64is disposed within the hollow roller 62 and is connected to a pair ofelectrical terminals 66 and 68 for energization from a suitable sourceof electrical energy to a temperature above that at which the principalhot-melt developer 14 melts. The peripheral surface 63 of roller 62 4 isin frictional contact with the peripheral surface 65 of the roller 17.

The roller 17 is also hollow and has a stationary electrical heatingelement 70 disposed therein. The heating element 70 is energized from asuitable source of electrical energy connected to a pair of terminals 72and 74. Energizing the heating elements 64 and 70 causes at least aportion of the principal hot-melt developer 14 to melt in the trough 60and to wet the surface 63 of the roller 62. The molten hot-meltdeveloper 14, which also wets the surface 65 of the roller 17 by contactwith the roller 62, is maintained in a liquid state on the heatedrollers 62 and 17 as the rollers are rotated by the driven roller 18.The liquified hot-melt developer 14 is applied to the photoconductiveinsulating surface 11 of the recording medium 12, at the developingstation 26, to develop the latent electrostatic image as the recordingmedium 12 is moved in the direction of the arrows 28 and 38.

During the developing operation for each latent electrostatic image, asmall portion of the principal hot-melt developer 14 is consumed and thequantity, as well as the level, of the hot-melt developer 14 in thetrough 60 consequently tends to decrease. The improved apparatus 10comprises means to maintain the quantity, and the level, of hot-meltdeveloper 14 in the trough 60 substantially constant. T 0 this end,there is provided a container 80, preferably of heat resistant,electrically insulating, plastic material, for holding a block or cake82 of replenisher hot-melt developer. The composition of the replenisherhot-melt developer 82 is substantially similar to that of the principalhot-melt developer 14.

In the embodiment shown in FIGS. 2, 3, and 4, the container issubstantially wedge-shaped for receiving therein a complementarywedge-shaped portion 84 of the block 82 of replenisher hot-meltdeveloper. The container 80 has a pair of opposite, parallel sides 86and 88, and a pair of opposite, downwardly and inwardly sloping sides 90and 92, as shown in FIG. 3.

A heating element 94, such as a strip of Nichrome wire, is disposedwithin the container 80 along the inner surfaces of the sides 90 and 92.One end of the heating element 94 is fastened to the inner surface ofthe side 90 by a rivet or screw 96, and the other end of the heatingelement 94 is fastened to the inner surface of the side 92 by a rivet orscrew 98. The rivets or screws 96 and 98 provide electrical contactmeans for electrical connectors 100 and 102, respectively, as shown inFIG. 3, for energizing the heating element 94 periodically in a mannerhereinafter to be described.

The container 80 is formed with a relatively small lower opening 104between the lower edges of the sides 90 and 92. A bight portion 106 ofthe heating element 94, intermediate the ends thereof, preferablyextends through the lower opening 104 of the container 80 to provide anintense concentration of heat for melting relatively small portions ofthe cake of replenisher hot-melt developer 82 and for directing themolten small portions to a desired target, the trough 60.

The conductors 100 and 102 may be connected to either the terminal XX,respectively, of the winding 56 or to the terminals YY, respectively, inparallel with connections to the projector 36, to energize the heatingelement 94 periodically. A variable resistor 108 (FIG. 1) may beinserted in series between the conductor 102 and either one of theterminals X or Y, if needed, for controlling the current through theheating element 94, thereby regulating its temperature to a desiredvalue.

The container 80 is disposed above the trough 60 by any suitable means,as by a bracket 109 (FIG. 3) fixed to the side 90 and to a suitable part(not shown) of the apparatus 10, so that replenisher hot-melt developer82, when molten, can flow through the lower opening 104 and fall intothe trough 60 to replenish the principal hotmelt developer 14 as thelatter is consumed.

In operation, the block or cake 82 of replenisher hot melt developer 82is inserted through a large upper opening 110 of the wedge-shapedcontainer 80 with the Wedge-shaped portion 84 of the cake in acomplementary in turn melts a small portion of the replenisher hot-meltdeveloper 82 adjacent to the heating element 94. Because of the sloping,wedge-shaped contours of the sides 90 and 92 of the container 80, themolten small portion of the replenisher hot-melt developer 92 fallsthrough the lower opening 104 onto the principal hot-melt developer 14in the trough 60. Also, as the block or cake of solid replenisherhot-melt developer 82 is consumed, it is advanced automatically, bygravity, into the container 80 so that a portion of it is alwaysadjacent the heating element 94.

Since the photoconductive insulating surface 11 of the recording medium12 is exposed each time it is desired to copy an image with theapparatus 10, the heating element 94 is energized each time theprojector 36 is energized, thereby melting a small portion of thereplenisher hot-melt developer 82 each time the recording element 12 isexposed with a light image. The portion 106 of the heating element 94that protrudes through the opening 104 provides an intense concentrationof heat and also directs the molten replenisher hot-melt developer 84 tothe trough 60. By controlling the current to the heating element 94 to adesired value, as by adjusting the variable resistor 108, it is possibleto add a small quantity of replenisher hot-melt developer 82 to theprincipal hotmelt developer 14 that is substantially the quantity ofprincipal hot-melt developer 14 consumed by the development of a typicalelectrostatic latent image at the developing station 26 during thedevelopment process. In this manner, it is possible to maintain thequantity, and thus the level, of the principal hot-melt developer 14 inthe trough 60 substantially constant during operation of the apparatusfor the development of a plurality of electrostatic images.

Instead of being connected to the terminals YY, the conductors 100 and102 can be connected to the terminals XX, respectively, of the coil 56.The variable resistor 108 is also connected in series with the conductor102 for adjusting the current through the heating element 94. Whenenergized from the coil 56, the heating element 94 is heated every timethe motor 19 is energized, that is, every time it is necessary to movethe recording element 12 in the process of making a visible copy of animage projected from the projector 36. Regardless of whether the heatingelement 94 is energized from the terminals XX or YY, however, it isapparent that the heating element 94 is energized periodically, that is,every time an image is produced on the recording medium 12.

Thus, there has ben shown and described an improved apparatus forreplenishing principal hot-melt developer with replenisher hot-meltdeveloper in an automatic electrophotographic system as the principalhot-melt developer is consumed. While the replenisher hot-melt developerhas been shown and described as a block or cake, it can also be in othersolid forms, such as solid granules, for example. Also, the heatingelement within the container for the replenisher hot-melt developer maybe energized intermittently or continuously from other components in theelectrophot-ographic system than from those described.

What is claimed is:

1. In apparatus for developing an electrostatic image on an insulatingsurface, wherein principal developer is a solid body comprisingfinely-divided electroscopic toner particles dispersed in anelectrically-insulating thermoplastic carrier material having a meltingpoint substantially within a range from 50 C. to 200 C., wherein saidsolid body is heated to melt at least a portion thereof, and whereinsaid molten portion is applied to said insulating surface to producethereon a visible image with said toner particles, the improvementcomprising:

a container for a quantity of melta-ble solid replenisher developer,said container having an upper opening, for receiving said replenisherdeveloper, and a lower opening,

heating means cooperatively associated with said container for heatingsaid container,

means connected to said heating means to energize said heating means andto melt at least a small portion of said replenisher developer, andmeans to dispose said container above said principal developer, wherebysaid molten portion of replenisher developer may emerge through saidlower opening for addition to said principal developer.

2. In apparatus for developing an electrostatic image as defined inclaim 1, said apparatus comprises:

a plurality of components adapted to be energized selectively from asource of electrical energy, and

said means connected to said heating means comprises means connected incircuit to at least one of said components to be energizedsimultaneously therewith.

3. In apparatus for developing an electrostatic image as defined inclaim 2, said one component is an electric motor.

4. In apparatus for developing an electrostatic image as defined inclaim 2, said one component is a light-image projector.

5. In apparatus for developing an electrostatic image as defined inclaim 1, at least a lower portion of the interior of said container iswedge-shaped, and said replenisher developer comprises at least a lowerportion that is wedge-shaped and adapted to conform to said interior ofsaid wedge-shaped container, whereby said replenisher developer may beadvanced by gravity into said container as portions of said replenisherdeveloper are melted.

6. In apparatus for developing an electrostatic image as defined inclaim 1, said heating means comprises a heating element, and a portionof said heating element extends through said lower opening of saidcontainer, whereby to direct said replenisher developer, when molten, ina desired direction.

7. In apparatus for developing an electrostatic image as defined inclaim 1, said apparatus is substantially automatic and comprises atrough for said principal developer, and heatable roller means disposedpartially within said trough to melt said principal developer and toapply said principal developer, when molten, to said insulating surfaceto develop said electrostatic image.

8. In apparatus for developing an electrostatic image on an insulatingsurface of a recording medium, wherein said apparatus comprises a troughfor principal hot-melt developer, a roller disposed within said trough,means to heat said principal hot-melt developer to melt it, and means toapply said molten principal hot-melt developer to said electrostaticimage to develop it, the improvement comprislng:

replenishing means for replenishing said principal hotmelt developer asit is consumed, said replenishing means comprismg a container forreplenisher hot-melt developer,

means to melt at least a portion of said replenisher hot-melt developerin said container, and

means to add said melted portion to said principal hotmelt developer,whereby to replenish said principal hot-melt developer.

9. In apparatus for developing an electrostatic image as defined inclaim 8,

said apparatus is substantially automatic and comprises a plurality ofcomponents adapted to be energized from a source of electrical energy,and

said means to melt a portion of said replenisher hotmelt developercomprises a heating element disposed within said container and connectedin circuit with at least one of said components for simultaneousenergization therewith.

10. In apparatus for developing an electrostatic image as defined inclaim 8,

said means to heat said principal hot-melt developer comprises a heatingelement disposed within said roller,

said means to apply said molten principal hot-melt developer to saidelectrostatic image comprise a second roller, in rolling contact withsaid first-mentioned roller, and means including a third roller disposedto move said recording medium between it and said second roller, and

said container comprises a lower opening therein,

whereby molten replenisher hot-melt developer may emerge therethroughfor addition to said principal hot-melt developer.

11. In apparatus for developing an electrostatic image as defined inclaim 8,

said container is wedge-shaped, having a relatively large upper openingfor receiving solid replenisher hot-melt developer, and a relativelysmaller lower opening through which molten replenisher hot-meltdeveloper may emerge for addition to said principal hot-melt developer.

12. In apparatus for developing an electrostatic image as defined inclaim 11, said solid replenisher hot-melt developer comprises at least aportion that is wedgeshaped and substantially conforms to the contour ofthe interior of said container, whereby said replenisher hot-meltdeveloper is advanced by gravity into said container as it is melted.

13. In apparatus for developing an electrostatic image as defined inclaim 8,

said container has a lower opening therein,

said means to melt at least a portion of said replenisher hot-meltdeveloper comprises a heating element disposed within said container,and

said means to add said portion to said principal hotmelt developercomprises means to dispose said container above said trough so that saidportion of replenisher hot-melt developer, when molten, may fall throughsaid lower opening for addition to said principal hot-melt developer.

14. In apparatus for developing an electrostatic image as defined inclaim 13,

said heating element in said container has a portion 10 which protrudesthrough said lower opening of said container, whereby to direct saidmolten portion of replenisher hot-melt developer to said trough.

15. Apparatus for feeding a hot-melt developer to a recording medium, inan electrostatic printing process,

said apparatus comprising:

(a) a first container from which hot-melt developer is applied to saidrecording medium,

(b) first heating means for melting developer material disposed in saidfirst container,

(c) a second container disposed above said first container and includingan opening at the bottom thereof through which developer material insaid second container may be discharged into said first container toreplenish the developer in said first container consumed by applicationto said recording medium, and

(d) second heating means for melting developer material disposed in saidsecond container.

References Cited UNITED STATES PATENTS PETER FELDMAN, Primary Examiner.

US. Cl. X.R.

